Controller of A.C. generator for vehicles

ABSTRACT

The structure of the present invention includes: a switching element inserted in series in a field coil of an A.C. generator for intermittently controlling a field current supplied to the field coil in accordance with an output voltage from the A.C. generator in order to control the output voltage from the A.C. generator to a predetermined value; and conduction rate control means for detecting a rotational speed of the A.C. generator to reduce a conduction rate of the switching element in accordance with an increase in rotational speed.

TECHNICAL FIELD

The present invention relates to a controller of an A.C. generator forvehicles.

BACKGROUND ART

A conventional controller of an A.C. generator for vehicles controlled aduty ratio of a switching element for intermittently controlling a fieldcurrent of a generator to thereby limit the field current so as for thefield current not to exceed a predetermined limitation value. Note that,the predetermined limitation value is selected so as to become a valueequal to or larger than a value of a field current which is to be causedto flow in order to obtain a predetermined output from the generatorwhen a temperature of a generator has risen up to a predetermined value(refer to JP 6-38720 B (page 2 and FIG. 1)).

In accordance with such a conventional controller for an A.C. generatorfor vehicles, there are shown generator output characteristics in whicha power transistor is usually held in a conduction state as long as agenerated voltage is lower than a predetermined value after a maximumvehicle electrical load has been put on a generator, and hence an outputis also increased in accordance with an increase in rotational speed ofthe generator. That is to say, there was encountered a problem such thattemperatures of an armature coil and a rectifier rose along with anincrease in output of the generator to become difficult to be suppressedwithin an allowable temperature, which resulted in reduction of quality.In addition, there was encountered a problem that a large cooling fanwas required as means for enhancing a cooling property in order tosuppress rise of a temperature, which resulted in that a generator couldnot be miniaturized.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above-mentionedproblems, and it is an object of the present invention that after therotational speed of the generator exceeds the predetermined value, anincrease in output of the generator is suppressed, whereby it ispossible to realize the miniaturized controller of an A.C. generator forvehicles (car, and the like) which is capable of preventing the heatingof the armature coil, the rectifier and the like, and hence whichrequires no cooling fan.

A controller of an A.C. generator for vehicles according to the presentinvention includes: a switching element inserted in series in a fieldcoil of an A.C. generator for intermittently controlling a field currentsupplied to the field coil in accordance with an output voltage from theA.C. generator in order to control the output voltage from the A.C.generator to a predetermined value; and conduction rate control meansfor detecting a rotational speed of the A.C. generator to reduce aconduction rate of the switching element in accordance with an increasein rotational speed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a circuit diagram of a controller of an A.C. generator forvehicles according to Embodiment 1 of the present invention;

FIG. 2 is a waveform chart showing a relationship between a waveform ofan input signal and a waveform of an output signal in a comparator ofthe controller of an A.C. generator for vehicles according to Embodiment1 of the present invention;

FIG. 3 is a graphical representation showing output currentcharacteristics of the controller of an A.C. generator for vehiclesaccording to Embodiment 1 of the present invention; FIG. 4 is a circuitdiagram of a controller of an A.C. generator for vehicles according toEmbodiment 2 of the present invention;

FIG. 5 is a circuit diagram of a concrete circuit configuration of atemperature detector shown in FIG. 4;

FIG. 6 is a circuit diagram of a concrete circuit configuration of atemperature detector shown in FIG. 4; and

FIG. 7 is a circuit diagram of a concrete circuit configuration of atemperature detector shown in FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferable embodiment modes of the present invention willbe described with reference to the drawings.

Embodiment 1

FIG. 1 is a circuit diagram of a controller of an A.C. generator forvehicles according to Embodiment 1 of the present invention. In FIG. 1,a generator for vehicles (hereinafter referred to as “a generator” forshort when applicable) 1 which is to be driven by an engine (not shown)has an armature coil 101 and a field coil 102. A rectifier 2 forsubjecting an A.C. output of the generator 1 to full wave rectificationhas a main output terminal 201 and a grounding terminal 202. Inaddition, a voltage regulator 3 for regulating an output voltage of thegenerator 1 to a predetermined value includes voltage division resistors301 and 302 for detecting a voltage which serve to voltage-dividing anoutput voltage obtained through the main output terminal 201 of therectifier 2 to detect a resultant voltage.

A constant voltage power supply circuit 300 provides a constant voltagesource A on the basis of an electric power which is supplied from abattery 5 by turning ON a key switch 4. A constant voltage of theconstant voltage source A is divided through voltage division resistors303 and 304 for generating a reference voltage to generate a referencevoltage. In addition, a comparator 305 compares the detected voltageobtained through the voltage division in the voltage division resistors301 and 302 for detecting a voltage with the reference voltage generatedthrough the voltage division resistors 303 and 304 for generating areference voltage. A power transistor (switching element) 307 isinserted in series in the field coil 102. As a current is supplied fromthe constant voltage source A to the power transistor 307 through aresistor 306, it causes the power transistor 307 to conduct, so a fieldcurrent is supplied to the field coil 102 in accordance with an outputof the comparator 305. An output voltage which has been outputtedthrough the main output terminal 201 by turning ON a load switch 6 issupplied to a vehicle electric load 7.

Moreover, the controller for an A.C. generator for vehicles according toEmbodiment 1 includes a conduction rate control circuit (conduction ratecontrol means) 312 for controlling a conduction rate of the powertransistor 307. The conduction rate control circuit 302 has an f-Vconverter 309 for converting a frequency proportional to a rotationalspeed obtained on the basis of one-phase output from the armature coil101 into a voltage, a triangular waveform generator 310 for generating avoltage having a triangular waveform, and a comparator 311 for comparingthe f-V conversion voltage value obtained through the f-V conversion inthe f-V converter 309 with the voltage having a triangular waveformgenerated from the triangular waveform generator.

Next, an operation of the controller for an A.C. generator for vehicleshaving the above-mentioned configuration will hereinafter be described.First of all, upon turn-ON of the key switch 4, an electric power issupplied to the constant voltage power supply circuit 300 to supply abase current from the constant voltage source A to the power transistor307 through the resistor 306. As the power transistor 307 conducts, itcauses the field current to flow through the field coil 102, so theengine (not shown) is started to drive the generator 1 to thereby startthe power generation.

The comparator 305 outputs an output signal at a “High” level when thedetection voltage of the generator 1 detected by the voltage divisionresistors 301 and 302 for detecting a voltage is lower in level than apredetermined value set using the resistors 303 and 304 for generating areference voltage, and outputs an output signal at a “Low” level whenthe detection voltage is higher in level than the reference voltage.

In addition, the f-V converter 309 outputs the f-V conversion voltagevalue which is obtained by converting the frequency proportional to therotational speed into voltage in response to the one-phase output signalfrom the armature coil 101. Here, an upper stage of FIG. 2 is a waveformchart showing a waveform of an input signal of the comparator 311, i.e.,a waveform of an output signal of the triangular waveform generator 310(an axis of abscissas represents an axis of time), and a waveform of anoutput signal of the f-V converter 309 (an axis of abscissas representsan axis of a rotational speed of the generator). Also, a lower stage ofFIG. 2 is a waveform chart showing a waveform of an output signal of thecomparator 311. As can be understood from FIG. 2, the comparator 311compares the voltage level of the f-V conversion voltage value with thevoltage level of the voltage having a triangular waveform generated bythe triangular waveform generator 310. Then, the comparator 311 outputsan output signal at a “High” level when after the rotational speed ofthe generator 1 has exceeded a predetermined rotational speed, thevoltage level of the f-V conversion voltage value does not exceed thevoltage level of the voltage having a triangular waveform, and outputsan output signal at a “Low” level when after the rotational speed of thegenerator 1 has exceeded a predetermined rotational speed, the voltagelevel of the f-V conversion voltage value exceeds the voltage level ofthe voltage having a triangular waveform.

Consequently, a rate (Low rate) of a period of time when the outputsignal is at a Low level continues to be increased in accordance with anincrease in rotational speed after the number of rotations of thegenerator 1 has exceeded a predetermined rotational speed. That is tosay, a conduction rate of the power transistor 307 will continue to bedecreased to reduce the field current. FIG. 3 is a graphicalrepresentation for comparison between output current characteristics ofgenerators controlled by the controllers for an A.C. generator forvehicles. In the FIGURE, a curve (a) represents the outputcharacteristics of the generator according to Embodiment 1 of thepresent invention, and a curve (b) represents the output characteristicsof a conventional generator. From FIG. 3 as well, it is understood thatthe output current of the generator according to Embodiment 1 issuppressed so as not to be increased even when the number of rotationsof the generator 1 exceeds the predetermined rotational speed.

As described above, according to the controller of an A.C. generator forvehicles of Embodiment 1 of the present invention, after the number ofrotations of the generator 1 has exceeded the predetermined rotationalspeed, the conduction rate of the power transistor 307 is reduced inaccordance with an increase in rotational speed to reduce the fieldcurrent, whereby it is possible to obtain the output currentcharacteristics in which even when the number of rotations of thegenerator 1 becomes equal to or larger than the predetermined rotationalspeed, the output current is suppressed so as not to be increased. Thus,the heating of the armature coil, the rectifier and the like can beprevented, and hence no cooling fan is required. Consequently,miniaturization can be realized.

Embodiment 2

Next, FIG. 4 is a circuit diagram of a controller of an A.C. generatorfor vehicles according to Embodiment 2 of the present invention. Thecontroller of Embodiment 2 has such a configuration as to newly providea temperature detector 313 in the conduction rate control circuit 312 inaddition to the constituent elements of the configuration shown inFIG. 1. FIGS. 5 to 7 show examples of concrete configurations of theabove-mentioned temperature detector 313. FIG. 5 shows the temperaturedetector 313 including a thermosensitive semiconductor element, FIG. 6shows the temperature detector 313 including a thermosensitiveresistance element having a positive resistance temperature coefficient,and FIG. 7 shows the temperature detector 313 including athermosensitive element having a negative resistance temperaturecoefficient.

The concrete configurations and operations of the temperature detectors313 will hereinafter be described.

In FIG. 5, a diode 312 a serving as the thermosensitive semiconductorelement and a resistor 312 b are inserted in series between the constantvoltage source A and the earth to be adapted to detect a temperaturechange voltage obtained on the basis of a change in temperature of thediode 312 a. In addition, voltage division resistors 312 c and 312 d,similarly, are inserted between the constant voltage source A and theearth to be adapted to generate a reference voltage from the constantvoltage source A. The reference voltage and the temperature changevoltage which are obtained in such a manner are compared with each otherin a comparator 312 e. Usually, the reference voltage (a minus inputvoltage of the comparator 312 e) is set so as to be higher than thetemperature change voltage (a plus input voltage of the comparator 312e), and hence the comparator 312 e outputs an output signal at a “Low”level. At the time when a temperature detected by the temperaturedetector 313 has exceeded a predetermined temperature, the plus inputvoltage of the comparator 312 e is increased in level due to negativetemperature characteristics of an internal voltage drop developed acrossthe diode 312 a to exceed the reference voltage (the minus inputvoltage), which results in that the comparator 312 e outputs an outputsignal at a “High” level.

In FIG. 6, a point of difference in configuration with FIG. 5 is that aresistor 312 f and a posistor 312 g serving as a thermosensitiveresistance element having a positive resistance temperature coefficientare provided for detection of the temperature change voltage instead ofthe diode 312 a serving as the thermosensitive semiconductor element andthe resistor 312 b. Note that, a resistor 312 f is connected to the sideof the constant voltage source A. Consequently, similarly to the case ofFIG. 5, the comparator 312 e normally outputs an output signal at a“Low” level. However, at the time when a temperature detected by thetemperature detector 313 has exceeded the predetermined temperature, theplus input voltage of the comparator 312 e is increased in level due topositive resistance temperature coefficient characteristics of theposistor 312 g to exceed the reference voltage (minus input voltage),which results in that the comparator 312 e outputs an output signal at a“High” level.

In FIG. 7, a point of difference in configuration with FIG. 6 is that athermistor 312 h having a negative resistance temperature coefficientand a resistor 312 i are provided instead of the resistor 312 f and theposistor 312 g serving as the thermosensitive resistance element havinga positive resistance temperature coefficient. Note that, conversely tothe case of FIG. 6, the thermistor 312 h is connected to the side of theconstant voltage source A. Consequently, similarly to the cases of FIGS.5 and 6, the comparator 312 e normally outputs an output signal at a“Low” level. However, at the time when a temperature detected by thetemperature detector 313 has exceeded the predetermined temperature, theplus input voltage of the comparator 312 e is increased in level due tothe negative resistance temperature coefficient characteristics of thethermistor 312 h to exceed the reference voltage (minus input voltage)As a result, the comparator 312 e outputs the output signal at a “High”level.

As described above, even if any of these temperature detectors 313 isused, when a temperature equal to or higher than the predeterminedtemperature is detected, the output signal at a “High” level isoutputted, and when a temperature does not rise up to the predeterminedtemperature, the output signal at a “Low” level is outputted.Consequently, since whenever the output signal at a “Low” level isoutputted from the temperature detector 313, the level of the outputsignal of the f-V converter 309 goes to “Low” to prohibit the outputcurrent of the generator 1 from being suppressed, the output currentcharacteristics of the generator 1 at this time becomes identical tothose of a conventional one. On the other hand, whenever the outputsignal at a “High” level is outputted from the temperature detector 313,the output signal of the f-V converter 309 becomes valid. Thus, if thenumber of rotations of the generator 1 exceeds the predeterminedrotational speed, then the operation for suppressing an increase inoutput current of the generator 1 is carried out. Consequently, thetemperature detector 313, only when a detected temperature is equal toor higher than the predetermined temperature, operates the f-V converter309.

As described above, according to the controller of an A.C. generator forvehicles of Embodiment 2 of the present invention, the temperaturedetector 313 is provided to thereby allow a temperature limitation to begiven.

INDUSTRIAL APPLICABILITY

According to the present invention, after the rotational speed of thegenerator exceeds the predetermined value, an increase in output of thegenerator is suppressed, whereby it is possible to realize theminiaturized controller of an A.C. generator for vehicles which iscapable of preventing the heating of the armature coil, the rectifierand the like, and hence which requires no cooling fan.

1. A controller of an A.C. generator for vehicles, comprising: aswitching element inserted in series in a field coil of an A.C.generator for intermittently controlling a field current supplied to thefield coil in accordance with an output voltage from the A.C. generator;and conduction rate control means for detecting a rotational speed ofthe A.C. generator to control a conduction rate of the switching elementin accordance with an increase in rotational speed, wherein theconduction rate control means comprises: an f-V converter that obtains avoltage through f-V conversion by converting a frequency proportional tothe rotational speed of the A.C. generator into a voltage; a comparatorfor controlling the conduction rate of the switching element inaccordance with a magnitude relationship between a level of the voltageobtained through the f-V conversion and a variable reference level.
 2. Acontroller of an A.C. generator for vehicles according to claim 1,wherein the conduction rate control means further comprises temperaturedetection means for detecting a temperature of a predetermined positionof the A.C. generator, and the temperature detection means, when adetected temperature is equal to or higher than a predeterminedtemperature, operates the f-V converter.
 3. A controller of an A.C.generator for vehicles according to claim 2, wherein the temperaturedetection means comprises a thermosensitive semiconductor element.
 4. Acontroller of an A.C. generator for vehicles according to claim 2,wherein the temperature detection means comprises a thermosensitiveresistance element having a positive resistance temperature coefficient.5. A controller of an A.C. generator for vehicles according to claim 2,wherein the temperature detection means comprises a thermosensitiveresistance element having a negative resistance temperature coefficient.